An Assessment of the Potential of Peptidoglutaminases I and II in Modifying the Charge Characteristics of Casein and Whey Proteins

Pepitidoglutaminases I and II of Bacillus circulans deamidate the yrcarboxyamide group of peptide-bound glutamine residues. Nucleic acid sequencing data indicate that, for many proteins, up to 50% of the residues originally reported as glutamate exist as glutamine. Thus an assessment of the potential of peptidoglutaminases I and II to modify the molecular parameters of proteins by altering their charge characteristics was undertaken. Peptido glutaminase I specifically deamidates the 7-carboxyamide group of glutamine at the car boxyl terminal of peptides. Peptidoglutaminase II, on the other hand, shows specificity for glutamine residues in peptide linkage. The limited applicability of peptidoglutaminase I was evident in that it was inactive against all proteins used as substrates.Peptidoglutaminase II, on the other hand, displays activity with small protein molecules containing glutamine residues. However, it is not active with larger proteins, such as the whey proteins and caseins, as substrates. Activity is detected against proteolytic digests of casein and whey proteins. Peptidoglutaminase II displays activity with peptidyl glutamine residues in molecules of molecular weight below 5000.